. Embryology. Embryology; Embryology; genealogy. EXCRETION IN EMBRYONIC DEVELOPMENT 255 which bring the circulating blood into contact with the oxygen dissolved in water. In addition, the frog embryo takes in dissolved oxygen through the skin, and the thin tail fins serve as additional surfaces for gaseous exchanges. In the chick embryo the increased surface necessary for respiratory exchange is provided by the development of the embryonic membranes. These were de- scribed in Chapter 12. The allantois and the yolk sac in particular provide an increased amount of surface which is important in t
. Embryology. Embryology; Embryology; genealogy. EXCRETION IN EMBRYONIC DEVELOPMENT 255 which bring the circulating blood into contact with the oxygen dissolved in water. In addition, the frog embryo takes in dissolved oxygen through the skin, and the thin tail fins serve as additional surfaces for gaseous exchanges. In the chick embryo the increased surface necessary for respiratory exchange is provided by the development of the embryonic membranes. These were de- scribed in Chapter 12. The allantois and the yolk sac in particular provide an increased amount of surface which is important in the oxygen intake and in carbon dioxide elimination of the embryo. During later development the allantois grows in size and fills in the space between the yolk sac and the shell. All the respiration of the embryo takes place by means of the allantois (Fig. 167). Excretion in embryonic development In the metabolism of proteins, urea and uric acid are formed and must be eliminated. The chick embryo has no way of getting rid of these excretions until the time of hatching. They must be stored within the shell. For a while, in the early period of development, the chick embryo excretes urea. Urea is a rather soluble substance and must be diluted by a large volume of water or it. SHELL ALLANTOIS Fig. 167. The allantois and its relation to the Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Barth, Lester G. (Lester George), 1905-1979. New York, Dryden Press
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